Turning
the volume up too high on your headphones can damage the coating of nerve
cells, leading to temporary deafness; scientists from the University of
Leicester have shown for the first time.

Earphones
or headphones on personal music players can reach noise levels similar to those
of jet engines, the researchers said.

Noises
louder than 110 decibels are known to cause hearing problems such as temporary
deafness and tinnitus (ringing in the ears), but the University of Leicester
study is the first time the underlying cell damage has been observed.

The
study has been published in the Proceedings of the National Academy of
Sciences.

University
of Leicester researcher Dr Martine Hamann of the Department of Cell Physiology
and Pharmacology, who led the study, said:

"The
research allows us to understand the pathway from exposure to loud noises to
hearing loss. Dissecting the cellular mechanisms underlying this condition is
likely to bring a very significant healthcare benefit to a wide population. The
work will help prevention as well as progression into finding appropriate cures
for hearing loss."

Nerve
cells that carry electrical signals from the ears to the brain have a coating
called the myelin sheath, which helps the electrical signals travel along the
cell. Exposure to loud noises - i.e. noise over 110 decibels - can strip the
cells of this coating, disrupting the electrical signals. This means the nerves
can no longer efficiently transmit information from the ears to the brain.

However,
the coating surrounding the nerve cells can reform, letting the cells function
again as normal. This means hearing loss can be temporary, and full hearing can
return, the researchers said.

Dr
Hamann explained: "We now understand why hearing loss can be reversible in
certain cases. We showed that the sheath around the auditory nerve is lost in
about half of the cells we looked at, a bit like stripping the electrical cable
linking an amplifier to the loudspeaker. The effect is reversible and after
three months, hearing has recovered and so has the sheath around the auditory
nerve."

The
findings are part of ongoing research into the effects of loud noises on a part
of the brain called the dorsal cochlear nucleus, the relay that carries signals
from nerve cells in the ear to the parts of the brain that decode and make
sense of sounds. The team has already shown that damage to cells in this area
can cause tinnitus - the sensation of 'phantom sounds' such as buzzing or ringing.

The
research was funded by the Wellcome Trust, Medisearch, GlaxoSmithkline and the
Royal Society.